The present invention relates to a packet ring network system, a packet transport method, an interlink node, a bypass pathway node, a program for an interlink node and a program for a bypass pathway node and, in particular, relates to a packet ring network system including three or more packet ring networks, a packet transport method applied to the packet ring network system, an interlink node, a bypass pathway node, a program for an interlink node and a program for a bypass pathway node.